Direct measurement of discrete valley and orbital quantum numbers in bilayer graphene

作者：Hunt B M; Li J I A; Zibrov A A; Wang L; Taniguchi T; Watanabe K; Hone J; Dean C R; Zaletel M; Ashoori R C; Young A F^*

来源：Nature Communications, 2017, 8(1): 948.

DOI：10.1038/s41467-017-00824-w

The high magnetic field electronic structure of bilayer graphene is enhanced by the spin, valley isospin, and an accidental orbital degeneracy, leading to a complex phase diagram of broken symmetry states. Here, we present a technique for measuring the layer-resolved charge density, from which we directly determine the valley and orbital polarization within the zero energy Landau level. Layer polarization evolves in discrete steps across 32 electric field-tuned phase transitions between states of different valley, spin, and orbital order, including previously unobserved orbitally polarized states stabilized by skew interlayer hopping. We fit our data to a model that captures both single-particle and interaction-induced anisotropies, providing a complete picture of this correlated electron system. The resulting roadmap to symmetry breaking paves the way for deterministic engineering of fractional quantum Hall states, while our layer-resolved technique is readily extendable to other two-dimensional materials where layer polarization maps to the valley or spin quantum numbers.

• 出版日期2017-10-16
• 单位Microsoft; MIT